The invention relates to disk access in scanner/printer control, and more particularly, to a technique for allocating disk bandwidth (BW) in order to prioritized disk access.
As electronic imaging machines such as copiers and printers become more complex and versatile in operation with greater speed and copy output required, there is a greater demand for higher performance and expectations from limited resources. A suitable control must be able to not only coordinate the operation of the various components of the machine such as the scanner and the printer but must also be able to schedule and allocate memory to provide the most efficient and productive operation of these components. In particular, in imaging machines there is often the need for various components of the machine such as the scanner or printer to have access to a mass memory device such as a disk memory. The disk capacity, often given as megabytes per second is a boundary that prevents unlimited access to the disk. Yet, many resources and components must often complete for disk access.
In the prior art, simple priority schemes such as a numerical round robin procedure are ineffective because they do not take into account the non uniform needs and capacity requirements of the differing resources and components requiring disk access with non-deterministic arrival rates. Some real time resources such as the printer or scanner need to be guaranteed a minimum amount of available disk bandwidth in order that data buffers can be emptied in time to be refilled. Other resources may simply attempt to access the disk simultaneously. A difficulty with the prior art machine systems is the lack of capability or control organization to meet these demands. It would be desirable to be able to provide a scheme to accurately limit the bandwidth allowed to some clients and guarantee the bandwidth to others.
It is an object, therefore, of the present invention to be able to coordinate simultaneous access to limited memory by multiple resources. Another object of the present invention is to guarantee real time resources a minimum amount of available disk bandwidth. Another object of the present invention is to allocate disk bandwidth between resources with realtime disk constraints and non-realtime performance requirements. Other advantages of the present invention will become apparent as the following description proceeds, and the features characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.